Increasingly, every meeting that I attend ends up dominated by one topic: the “hash of the email address.” But for now, it’s a one-sided discussion.

While the folks I meet with tend to be somewhat technically oriented, most of them are business people focused on the sales – not technical – side of their enterprise. Every single one of them knows what a cookie is and understands the difference between a first- and third-party cookie. But when it comes to “hashing emails,” I am mostly met by blank stares or questions.

It’s exciting and challenging to be working with something new. It reminds me of the early days of email marketing when people would ask why they should build an email list and why they should send emails to their customers. Nowadays, the question is moot in regards to the “why” of email marketing.

But, compared to the cookie, almost no one knows about the power of the MD5 hash of the email address.

I’ll offer the first prediction for 2014: everyone professionally engaged in interactive marketing is going to know about email hashes and why they’re important – and today you’re going to get a leg up on your competition.

So, what’s an MD5 hash?

An MD5 hash is a “cryptographic function.” It takes an arbitrary piece of data, like an email address, and converts it to a 32-character hexadecimal string. Every time you run the same piece of data through the hashing algorithm you get the same result. What that means is that your email address – a unique value – is converted to a unique hash string through this process. Originally used as a security feature, it’s now surprisingly ended up as a marketing tool – and a really cool one that works across every marketing channel in use today.

“Hashing” an email address is a very simple process. Here are the ingredients:

An email address like dave@liveintent.com

An MD5 hash algorithm application – there are dozens of free apps for this, just search for “MD5 hash programs”

Run the email address through the MD5 algorithm

Out pops a one-way, unique value (in this case: dave@liveintent.com converts to 43307bb5a669b247270a4d81cce6f3ff)

What can you do with an email hash? There are tons of applications.

Dedicated email campaigns. Standalone third-party advertisements within publisher newsletters are still a popular way to reach your audience, but most advertisers do not want to mail to your whole list. Advertisers can send over a “hold-out” list consisting of MD5 hashes, match them to the publisher’s file, and suppress the matching results. Using this approach, the parties share no actual email addresses, and since the hashes can’t be converted back to actual email addresses, the hashes are useless for any purpose other than matching.

Want to make sure your loyal customer gets the best deal? Target her using hashes. Want to market to prospects? Suppress your customers using hashes.

Custom audience campaigns. Facebook and now Twitter have implemented or announced the availability of “custom audience” targeting programs. Custom audience campaigns are dependent upon email hashes or hashed phone numbers for their targeting. When you log in to Facebook or Twitter, you are doing so with either an email address or a phone number. Marketers can load up segments consisting of hashed values (customer lists, for example) and when they match users, can bid for them and present an ad in the news feed or within Twitter clients like TweetDeck.

Email ad exchanges. By leveraging the power of the email hash, advertisers can now reach their customers with a loyalty message and their prospects with a prospecting message. Thousands of newsletters from hundreds of top publishers now feature “email addressable audiences” via hash-based targeting. Targeting only the hashes you want reduces waste and increases response rates.

And this is only the tip of the iceberg. We are just beginning to understand the power and potential of the email hash. In my next column I will cover techniques for multi-channel customer targeting using email hashes.